The present invention relates to a wheel loader.
A wheel loader is generally used to excavate a natural ground with a bucket and load it into a dump truck. FIG. 4 shows a series of driving pattern from excavation of a wheel loader 101 to loading into a dump track 103, and this is a driving pattern called V-shape driving, which is the most frequently used (for example, Japanese Patent Application Publication No. 7-39675). Specifically, the wheel loader 101 travels forward to a natural ground 102 in a forward second speed gear (F2) (driving W1). When it approaches the natural ground 102 (0.5 m to 1.0 m), it thrusts into the natural ground 102 in a forward first speed gear (F1) in order to increase tractive force for the case in which an excavating operation is performed (driving W2). When the excavation is finished, the wheel loader 101 is retreated from an excavating operation position at a high speed in a reverse second speed gear (R2) (driving W3). Subsequently, a traveling direction of the wheel loader 101 is changed, and make it approach the dump truck 103 at a high speed in F2 (driving W4). When a loading operation for the dump truck 103 is finished, the wheel loader moves away from the dump truck 103 at a high speed in R2 (driving W5).
The V-shape driving is performed in a cycle time of about 30 seconds. In one cycle, the wheel loader moves forward and rearward twice, and it is general to perform a forward and reverse travel switching operation during traveling with use of vehicle inertia absorption action in fluid coupling such as a torque converter at a time of switching forward and reverse travel to shorten the cycle time during an operation. For example, when it shifts from the driving W3 to the driving W4, an operator returns an accelerator at a speed near to the maximum speed during revere traveling of the driving W3, switches the gear from reverse to forward travel by a shift operation, and depresses an accelerator pedal to decelerate with engine output power. A brake pedal is operated to such an extent as to be pressed lightly.
However, the aforementioned prior art has the disadvantages that will be described hereinafter. Specifically, deceleration during reverse travel is performed by an accelerator operation in the shift to forward travel, and deceleration during forward travel is performed by an accelerator operation in the shift to reverse travel with use of engine output power, and therefore fuel economy becomes unsatisfactory, a large-sized radiator is needed due to the problem of heat balance.
When it shifts to the driving W4 after the engine revolution reduces, the vehicle
(1) performs a steering operation,
(2) performs a boom raising operation in loading,
(3) accelerates a vehicle body forward, and
(4) accelerates an engine itself
at the same time, and therefore the output power of the engine becomes insufficient to impair start-up of engine revolution, which sometimes causes poor acceleration.
The present invention is made in view of the above-described disadvantages, and its object is to provide a wheel loader, which reduces fuel consumption and which is excellent in accelerating ability, eliminating lack of output power of an engine.
In order to attain the above-described object, a first aspect of the wheel loader according to the present invention has a structure in which in a wheel loader performing operations by driving an hydraulic pump for driving a working machine and driving wheels of a vehicle by an engine, the wheel loader includes
a first electric motor capable of transmitting torque to the driving wheels,
electricity accumulation means for transferring electric energy to and from the first electric motor, and
a controller for controlling a generating operation of the first electric motor that receives torque transmission from the driving wheels and generates electric power at the time of a decelerating operation of the vehicle, and storing generated electric energy into the electricity accumulation means.
According to the above structure, regenerative braking is carried out by the first electric motor at the time of the decelerating operation of the vehicle, and kinetic energy held by the vehicle is converted into electric energy and stored. Consequently, it is not necessary to use engine output power to decelerate as in the prior art, thus improving fuel economy, and making it possible to reduce the size of the radiator as a result of improvement in heat balance.
Further, the wheel loader may have the structure in which the controller controls discharge of the electric energy stored in the electricity accumulation means, and controls a motor operation of the first electric motor to transmit torque to the driving wheels, at the time of an accelerating operation of the vehicle.
According to the above structure, with use of the electric energy stored in the electricity accumulation means by regenerative braking, the motor operation of the first electric motor is performed at the time of an accelerating operation of the vehicle to assist engine output power to drive the driving wheels. As a result, the load on the engine is reduced and lack of output power can be prevented and accelerating ability of the vehicle can be improved.
Further, the wheel loader may have the structure in which the wheel loader includes a second electric motor capable of transmitting torque to the hydraulic pump, and in which
electricity accumulation means is capable of transferring electric energy to and from the second electric motor, and the controller controls discharge of the electric energy stored in the electricity accumulation means, and controls a motor operation of the second electric motor to transmit torque to the hydraulic pump, at the time of operating a working machine of the vehicle.
According to the above structure, with use of the electric energy stored in the electricity accumulation means by regenerative braking, the motor operation of the second electric motor is performed at the time of operating the working machine of the vehicle to assist the engine output power to drive the hydraulic pump, thus reducing the load on the engine and making it possible to prevent the lack of the output power.
Further, the wheel loader may have a structure in which the wheel loader includes a resister capable of being connected to the first electric motor, and in which the controller has function of detecting a charge amount of the electricity accumulation means, and
supplies electric energy generated by the first electric motor to the resistor when the controller detects that the charge amount of the electricity accumulation means reaches full charge.
According to the above structure, when the charge means reaches the full charge, the electric energy generated as a result of regenerative braking can be consumed in the resister, and therefore even if the electricity charge means is the full charge, regenerative braking is possible. Accordingly, it is not necessary to use engine output power to decelerate as in the prior art, and fuel economy is improved and the radiator can be reduced as a result of improvement in heat balance.
A second aspect of the wheel loader according to the present invention has a structure including
an engine,
a generator driven by the engine,
electricity accumulation means for storing electric energy generated by the generator,
a first electric motor capable of transferring the electric energy to and from the electricity accumulation means and transmitting torque to driving wheels of a vehicle,
a second electric motor capable of transferring the electric energy to and from the electricity accumulation means and transmitting torque to a hydraulic pump for driving a working machine, and
a controller for controlling a generating operation of the first electric motor that receives torque transmission from the driving wheels and generates electric power, and storing generated electric energy in the electricity accumulation means, at the time of a decelerating operation of the vehicle.
According to the above structure, regenerative braking is performed by the first electric motor at the time of a decelerating operation of the vehicle, and the kinetic energy held by the vehicle is converted into the electric energy and stored. Consequently, since it is not necessary to use engine output power to decelerate as in the prior art, fuel economy is improved, and the radiator can be reduced in size as a result of improvement in heat balance.